Animal Altruism Altruism occurs when the giver suffers a fitness loss while the recipient experiences a fitness gain. “Loss” could be trivial (you wasted seconds of my time) or significant (sacrificed my life) Peter Kropotkin 1842-1921, Russia • Born Prince Kropotkin, became disgusted with contrast between the extravagances of court life and the poverty of Russian peasants. • Studied biology and geography; volunteered for expedition to eastern Siberia. Expected Darwin’s prediction of competition, instead saw cooperation in both society and nature. • Published Mutual Aid: A Factor of Evolution in 1890 as a rebuttal to T.H. Huxley and other social Darwinists. • Travels to join international workers movements; survives prison in Russia, assassination in London, arrest in Paris. deportation from Switzerland. In 1917 returns to Russia for revolution, but stops when the Bolsheviks come to power. Some of Kropotkin’s examples can be explained away by “kin selection” Since worker bees are sterile clones, its easy to see how they can sacrifice their life and still propagate their genes. It is not so much “altruism” on the part of the bee but rather selfish selfinterest on the part of the genes. Hence the title of Dawkin’s book, “The Selfish Gene” Some of Kropotkin’s examples can be explained away by “kin selection” You share ½ your genes with a sibling, 1/8th with cousin. r = the genetic relatedness of the recipient to the giver B = reproductive benefit gained by the recipient C = the reproductive cost to giver Kin selection predicts rB > C must hold for altruism to occur J.B.S. Haldane: “I would willingly die for two brothers or eight cousins.” Red squirrels: surrogate mothers adopt related orphaned squirrel pups but not unrelated orphans. Cost = decrease in survival probability of the litter. Benefit = increased chance of survival of the orphan. Females always adopted orphans when rB > C, but never adopted when rB < C. Some of Kropotkin’s examples CANNOT be explained away by “kin selection” • Dogs often adopt orphaned cats, squirrels, ducks, etc. • Dolphins support sick or injured animals in water • Chimpanzees will help humans and conspecifics without any reward in return. • Birds such as Mexican Jays will help feed young unrelated to them. • Birds will given alarm calls in flocks of mixed species. • Lemurs of all ages and of both sexes will take care of infants unrelated to them. Inter-species altruism Osprey feeding Slender Billed Gull (BBC). Perhaps a “pathology”? Is nature as ruthlessly competitive as evolutionary biologists have theorized? Perhaps altruism can “err on the side of caution” and still be an Evolutionarily Stable Strategy. What if we “cooperate on the first move”? The Iterated Prisoner’s Dilemma winner: Rapoport’s tit for tat The first time meeting a program, cooperate The next time, repeat what it did last time. If T4T meets itself, they cooperate If T4T meets defect-only, it only gets fooled once If T4T meets random chooser who defects, (eg JOSS), it will retaliate on the next move (often when JOSS cooperates, thus lowering JOSS score) Many variations on this are possible: “tit for two tats” for example. All must cooperate first, retaliate eventually, and forgive eventually to qualify. Something like tit-for-tat may be at work in cases of “reciprocal altruism” Monkeys: individuals which are groomed are much more likely to groom or support their groomers than monkeys that had not groomed. However grooming also varies depending on rank, stress, etc. “Biological Market Model” Tit-for-Tat Bats The vampire bat: individuals which feed blood are much more likely to get fed themselves. Distribution of risk: best place to store extra food is in the belly of your neighbor One fish, two fish, cooperate with you fish Stickleback fish: “scouting” near potential predator is a risk, but helps group determine when it is safe to leave for hunting. Stickleback are more likely to do scouting if they have evidence of other scouts: recall Orstom’s “contingent cooperators” Reciprocal altruism in interspecies cooperation: cleaner wrasse • Cooperating: Cleaners eat ectoparasites, clients benefit from being cleaned • Defecting: cleaners eat client mucus/tissue instead of parasites; clients eat cleaners • Threat of retaliation increases cooperation: Predatory clients are cheated less often than nonpredatory clients because they cast a “shadow of the future”. Cleaners who cheat are chased away. • A biological market: reputation effects determine levels of service Acorn Woodpecker Acorn Woodpecker: Why don’t “free riders” rise in genetic frequency? Recall Orstom’s “clearly defined boundaries”: a group of cooperators could out-compete a group of non-cooperators (Nowak).